MESFETs (metal-semiconductor field effect transistor) and HEMTs (high electron mobility transistors) are usually constructed in compound semiconductor technologies, and are faster but more expensive than silicon-based JFETs or MOSFETs (metal-oxide-semiconductor field-effect transistor). MESFETs are commonly used for microwave frequency communications and radar. For example, MESFETs/HEMTs can be used in cascode circuits for cellular power amplifier applications. However, it is increasingly difficult to use MESFETs as the basis for integrated circuits as the scale of integration increases, compared to CMOS silicon based fabrication.
MOSFETs are typically used for amplifying or switching electronic signals. MOSFETs are voltage-controlled power devices; that is, if no positive voltage is applied between gate and source the MOSFET is always non-conducting (enhancement mode MOSFET). For depletion mode MOSFET, the MOSFET is conducting even if the applied voltage between gate and source is zero. Although the MOSFET is a four-terminal device with source (S), gate (G), drain (D), and body (B) terminals, the body (or substrate) of the MOSFET is often connected to the source terminal, making it a three-terminal device like other field-effect transistors.